[jit] Renamed prim::Concat as prim::VarConcat (#61983)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61983
Trial #2. The previous PR (https://github.com/pytorch/pytorch/pull/61498) was reverted because this caused a failure in `pytorch_linux_backward_compatibility_check_test`. Fixed that now by adding to the exception list in `check_backward_compatibility.py`.
Test Plan: Imported from OSS
Reviewed By: eellison
Differential Revision: D29828830
Pulled By: navahgar
fbshipit-source-id: 947a7b1622ff6e3e575c051b8f34a789e105bcee
